This application relates generally to geophysical exploration, and more specifically to seismic data acquisition and sensor technologies. In particular, the application relates to sensor systems for marine seismic surveys, including, but not limited to, ocean bottom cables and autonomous seismic node applications.
Petrochemical products are ubiquitous in the modern economy, and can be found in everything from oil and gasoline to medical devices, children's toys, and a wide range of everyday household items. To meet the continuing demand for these products, oil and gas reserves must be accurately located and surveyed, so that these important resources can be effectively managed. As a result, there is an ongoing need for new seismic sensor systems and more advanced exploration technologies.
Scientists and engineers typically utilize seismic wave-based exploration to locate new oil and gas reservoirs, and to survey and manage existing reserves over time. Seismic surveys are performed by deploying an array of seismic sensors or receivers over the region of interest, and monitoring the response to controlled emission of seismic energy via a seismic source such as a vibrator, air gun array, or explosive detonation. The response depends upon the seismic energy reflected from mineral reservoirs and other subsurface formations, allowing an image of the corresponding structures to be generated.
Conventional marine seismic surveys typically proceed by towing an array of seismic sensors or receivers behind a survey vessel, with the receivers distributed along one or more streamer cables. A set of air guns or other seismic sources is used to generate the seismic energy, which propagates down through the water column to penetrate the ocean floor (or other bottom surface). A portion of the seismic energy is reflected from subsurface structures, and returns through the water column to be detected in the streamer array. Alternatively, seismic receivers can also be disposed along an ocean-bottom cable, or provided in the form of individual, autonomous seismic nodes distributed on the seabed.
Seismic receivers include both pressure sensors and particle motion detectors, which can be provided as individual sensor components or combined together with both sensor types provided in close proximity within a receiver module or seismic node. For example, a set of pressure sensors can be configured in a hydrophone array, and adapted to record scalar pressure measurements of the seismic wavefield propagating through the water column or other seismic medium. Particle motion sensors include accelerometers and geophones, which can provide single-axis or three-dimensional vector velocity measurements that characterize motion of the medium in response to propagating seismic waves.
Geophysical data pertaining to subsurface structures is acquired by observing the reflected seismic energy with an array of such receiver components. The resulting seismic signals can be used to generate an image characterizing the subsurface composition and geology in and around the survey area. The overall image quality depends on noise and signal sensitivity, creating a demand for more advanced sensor and receiver technologies.